The present invention relates to multiwall, gusseted, stepped end bags and is particularly directed to improvements in bags as disclosed in U.S. Pat. No. 3,650,460 and other related patents. The type of bag disclosed herein is generally referred to in the industry as a pinch style bag because of its unique end closure.
Pinch style bags are well suited for packaging most materials but in particular, they are useful for packaging granular, free flowing products, products requiring a high degree of moisture protection and food grade products that require protection from infestation and contamination that may be caused by leakage and sifting of the packaged product. However, most prior art pinch style bags are of the open mouth type which can only be filled with open mouth filling equipment, and, such filling equipment tends to increase the aeration of fine powdery products which produces air release problems after the bags are sealed. Moreover, use of the open mouth pinch style bags of the prior art requires that each bag user have his own end sealing equipment.
To offset some of the problems inherent with the filling of fine powdery materials into an oen mouth pinch style bag, valved bags such as pasted end valved bags were adopted. These bags solved some of the filling problems such as decreased aeration of the product and the concurrent air release problems. However, the use of pasted end valved bags introduced severe leaking and sifting conditions that could not be tolerated, particularly when packaging food grade products. Accordingly, the bag of the present invention was developed to overcome the filling problems of prior open mouth pinch style bags and the leaking and sifting problems with prior art pasted end valved bags. Thus, the gusseted, stepped end, pinch style valved bag of the present invention with its integral valve and pinch style closure provides a filling versatility heretofore not available to pinch style bag users and a positive stepped end closure for improved resistance to leakage and sifting not previously achieved with pasted end valved bags.